A State Department spokesman expressed alarm Tuesday over Iran's admitted program of uranium enrichment and declared outright that Terhan was defying the world with an "unrelenting push toward nuclear weapons capability."

But neither President George W. Bush nor his Democratic challenger John Kerry had any immediate reaction Wednesday. A Kerry spokesman, when asked for comment, called the situation "another national security failure" for the Republican administration.

Spokesman Mark Kitchens said Bush's "arrogant unilateralism" made it harder to get support within the International Atomic Energy Agency (IAEA) to refer Iran to the UN Security Council for possible sanctions.

"We must make clear to Iran that the United States will lead an international effort to push for tougher measures, including sanctions, if they do not comply with the IAEA resolution," Kitchens told AFP.

Despite his remarks, neither side gone out of its way to make Iran an issue in the November 2 election, a passivity that contrasts sharply with the heated rhetoric over Iraq.

Bush argues that Saddam Hussein's mere intention to develop nuclear arms justified the invasion last year to oust him. But Iran, another member of his "axis of evil," never came up in a major speech Tuesday to the United Nations.

The 21-minute address made one just passing reference to his determination to "prevent proliferation" as part of his war on terror keyed by the military operations in Afghanistan and Iraq.

Both Kerry and Bush have publicly attached the highest priority to preventing the spread of nuclear, chemical and biological weapons. But neither side has spelled out how they would handle continued intransigence by Iran.

Nor have they even hinted at the possibility of eventual military action to prevent Tehran from developing a nuclear weapons capability. Asked about the prospect Wednesday, Kitchens declined to comment.

Kerry appeared to have hardened his position on Iran since December when he proposed bilateral talks "to explore areas of mutual interest with Iran, just as I was prepared to normalize relations with Vietnam a decade ago."

By June he seemed to be soft-pedalling the idea as he declared: "a nuclear armed Iran is unacceptable. An America, whose interest and allies could be on the target list, must no longer sit on the sidelines."

The Massachusetts senator called for strengthening the Nuclear Nonproliferation Treaty and suggested Washington "call their bluff" when the Iranians say they are merely trying to meet their domestic energy needs.

"We should ... organize a group of states that will offer the nuclear fuel they need for peaceful purposes and take back the spent fuel so they can't divert it to build a weapon. If Iran does not accept this, their true motivations will be clear."

The administration has not picked up on the idea but Bush insisted last month "we are paying very close attention to Iran. ... We are working with our friends to keep the pressure on the mullahs to listen to the demands of the free world."

The Bush administration has stayed away from any detailed explanation why it was willing to go after Saddam's alleged nuclear arsenal but was not ready to brandish the threat of force against Iran.

"Different threats require different strategies," the president said in his State of the Union address to Congress last year.